Config file syntax: secrets from file in key=value

[Tobias Florek]

Hi Aki!

 > You can use $ENV:variable syntax with Dovecot v2.3.14+. The 
environment variable needs to be listed in `import_environment` setting 
and be available for dovecot process on startup.

Thank you for your answer.  I will test it tomorrow.

I thought it was not supported because I interpreted

 > Expansion only works when it’s surrounded by spaces.

as it not being able to use for e.g.

default_fields = pass=$ENV:MY_ENV_VARIABLE

If it does indeed work I will submit a pull request clarifying the 
documentation.

Cheers,
  Tob